Cigarette smoke (CS) suppresses the immune system, and smoking is the major risk factor for chronic obstructive pulmonary disease (COPD). Exposure to cigarette smoke is associated with a significant increase in the risk for respiratory viral infections. Our work is to understand how CS compromises the human innate immune system's response to influenza virus infection, and to find novel methods to control the infection. Epidemiological studies show that influenza infection is seven times more common and is much more severe in smokers than nonsmokers. Retinoic acid-inducible protein I (RIG-I) plays an important role in the recognition of, and cytokine induction by, influenza virus and other RNA viruses. Our previous studies, using an ex vivo human organ culture model, have found that cigarette smoke extract (CSE) suppresses antiviral and innate immune responses in influenza virus infected human lung through oxidative inhibition of viral-mediated induction of the pattern recognition receptor, RIG-I. This immunosuppressive effect of CS may play a role in the enhanced susceptibility of smokers to serious influenza infection in the lung. We propose to use an in vivo mouse model to study the mechanism by which CS suppresses the expression and function of the RIG-I initiated innate response to influenza virus. The hypothesis of this proposal is that long-term CS impairs the protective RIG-I initiated antiviral response to influenza virus in vivo while RIG-I overexpression and antioxidants provide therapeutic inhibition of immunosuppression from smoking. To test the central hypothesis, we propose to pursue the following integrated specific aims: AIM 1: Is RIG-I knockdown by CS responsible for the suppression of the RIG-I initiated antiviral response in CS-exposed mice? AIM 2: Can RIG-I overexpression in mouse lung reverse the CS-mediated suppression of the antiviral response in CS-exposed mice? AIM 3: Can antioxidants restore the RIG-I initiated antiviral response in CS-exposed mice? These studies will significantly enhance our understanding of the mechanism whereby CS suppresses the human immune system and predisposes humans to worse outcomes of influenza virus infection. Determination of the molecular mechanisms of immunosuppression will be important in designing strategies for the development of new and novel treatments for cigarette smoke enhanced lung infections, particularly those due to influenza.